Jeong-Seek Kang

An Experimental Study on Flow in the Nozzle of a Radial Turbine

Experimental study on the flow field inside the nozzle for radial turbine was performed. At design point, the pressure is high and the Mach number is low at the pressure side of the nozzle inlet semi-vaneless space as the flow turns through the nozzle vanes. As the flow accelerates through the nozzle passage to the throat the pressure level at the pressure and suction sides becomes similar. The flow continued accelerating from the throat to the inlet of turbine wheel and the pressure field became uniform in the circumferential direction in the vaneless space. In high expansion ratio condition, strong favorable pressure gradient band region occurred just after the throat in the semi-vaneless space in the circumferential direction and the pressure became uniform in the circumferential direction after this band. In low expansion ratio condition, core flow acceleration is dominant after the throat and this non-uniform pressure field reached to the inlet of turbine wheel.

Thermodynamic and aerodynamic meanline analysis of wet compression in a centrifugal compressor

Wet compression means the injection of water droplets into the compressor of gas turbines. This method decreases the compression work and increases the turbine output by decreasing the compressor exit temperature through the evaporation of water droplets inside the compressor. Researches on wet compression, up to now, have been focused on the thermodynamic analysis of wet compression where the decrease in exit flow temperature and compression work is demonstrated. This paper provides thermodynamic and aerodynamic analysis on wet compression in a centrifugal compressor for a microturbine. The meanline dry compression performance analysis of centrifugal compressor is coupled with the thermodynamic equation of wet compression to get the meanline performance of wet compression. The most influencing parameter in the analysis is the evaporative rate of water droplets. It is found that the impeller exit flow temperature and compression work decreases as the evaporative rate increases. And the exit flow angle decreases as the evaporative rate increases.

Aerodynamic Rig Test of Radial Turbine for APU

175.74mm . 터빈 입구에서의 상세 유동이 측정되었다 노즐의 허브면에서 측정한 압력과 노즐의 쉬라우드 면과 터 . 빈 휠 케이싱에서 측정한 압력 분포를 볼 때 터빈 내부에서의 팽창과정이 적절함을 확인할 수 있었다. Abstract: An aerodynamic rig test of a radial turbine for an auxiliary power unit (APU) was performed at a high-temperature turbine test facility at the Korea Aerospace Research Institute. The pressure ratio, Mach number, and flow coefficient in the rig test are the same as those under normal engine operation conditions. The design pressure ratio is 3.096, design test speed is 34909 rpm, and turbine inlet temperature is 160°C. The turbine has airfoil-type nozzles, and the diameter of the turbine wheel is 175.74 mm. The turbine map is experimentally measured, and the detailed flow at the turbine inlet is measured. The pressure distribution in the nozzle at both the hub and the shroud sides and the pressure distribution along the shroud casing of the turbine wheel were measured, and this confirmed that the expansion process in the turbine wheel is acceptable.

Modeling and Experimental Evaluation on Torque Loss in Turbine Test Rig

To evaluate the performance of a turbine through turbine rig test, torque or power generated from the test turbine should be measured. This is measured from a dynamometer or torquesensor installed in the test rig. So, to evaluate the performance of turbine with high precision, the accurate measurement of power or torque is necessary. However, there is an intrinsic difficulty as not all the power generated by the turbine is measured by the dynamometer or torquesensor. A small portion of power generated from test turbine is dissipated through bearing loss and windage loss. This dissipated energy is called mechanical loss of test rig. Therefore, it is necessary to measure the mechanical loss of the test rig for the accurate evaluation of the turbine performance. This paper divides mechanical loss as bearing loss, disk windage loss and extra windage loss. Spin down tests are performed in a 1-stage axial turbine test rig to evaluate each losses. It is found that the dominant loss is bearing loss and the total mechanical loss amounts to 0.78∼1.4% of energy generated at the turbine. And the effect of bearing temperature is investigated and it is found that the mechanical loss is dependent on the bearing temperature and that it increases with decreasing bearing temperature.Copyright

Performance Test of Centrifugal Compressor for Microturbine with Running Tip Clearance

Tip clearance of centrifugal compressor affects the performance. Larger tip clearance results in lower efficiency. What really affects the performance is the running tip clearance, not the cold tip clearance. When the compressor is operating, blade strain and the pressure difference between impeller backplate and hub affects the running tip clearance. This paper describes measured running tip clearance and its effects on the performance of centrifugal compressor. Cold tip clearance before operation was 0.4 mm and running tip clearance varied from 0.86 mm to 0.25 mm with impeller exit pressure. As the pressure at impeller exit increases, the running tip clearance tends to decreases. The target running tip clearance for Compressor at speed was 0.3 mm, and it turned out to be exactly 0.30 mm from experiment.

Review of Stall Inception in Turbocompressors

Stall inception means the phenomena of rotating stall initiation. The initiation mechanism of rotating stall, the existence of stall precursor, the behavior of stall precursor, stall warning scheme and control scheme are the main interests in stall inception research. Compared to the studies on rotating stall which has long history, the stall inception has been studied for about recent 20 years. After the first discovery of stall precursor in about 20 years ago, many studies were reported on stall inception phenomena. The inception pattern of `mode` and `spike` were found, and some of its characteristics are known. And now the stall inception has become one of the fascinating fields in turbomachinery. The development stall control scheme which apply the reliable stall warning scheme will play a great role in future compressor and aeroengine. This paper reviews the results and analysis methods on stall inception studies.

Development of a performance prediction method for centrifugal compressor channel diffusers

A hybrid performance prediction method is proposed in the present study. A channel diffuser is divided into four subregions: vaneless space, semi-vaneless space, channel, and channel exit region. One-dimensional compressible core flow and boundary layer calculation of each region with an incidence loss model and empirical correlation of residuary pressure recovery coefficient of a channel predict the performance of diffusers. Three channel diffusers are designed and tested for validating the developed prediction method. The pressure distributions from an impeller exit to the channel diffuser exit are measured and discussed for various operating conditions from choke to nearly surge conditions. The strong non-uniform pressure distribution which is caused by impeller-diffuser interaction is obtained over the vaneless and semi-vaneless spaces. The predicted performance shows good agreement with the measured performance of diffusers at a design condition as well as at off-design conditions.